Lightweight Mrrm with Radio Agnostic Access Selection in the Core Network

ABSTRACT

A method and arrangement for making a handover decision in a multi-access communication network is disclosed. A first set of criteria is determined for when a handover between at least two access paths should be performed and a report is sent when at least one criterion of a first set of criteria is fulfilled. A second set of criteria is determined for when a handover between said at least two access paths should be performed and a report is sent when at least one criterion of said second set of criteria is fulfilled. One or more data sessions of at least one user terminal network are determined to be handed over based on the sent reports and a core network anchor and a terminal anchor are directed to execute a handover by re-routing said determined data sessions from one access path to an alternative access path.

TECHNICAL FIELD

The present invention relates to the field of multi-access communicationnetworks and, particularly, to an arrangement allowing for making ahandover decision in a multi-access communication network as well as amethod for such decision. The invention further relates to a computerprogram product for performing the method.

BACKGROUND OF THE INVENTION

It has been shown in several studies that joint management of differentradio access technologies, such as multi-radio resource management(MRRM) can bring substantial gain to network capacity and userperformance in a multi-access network. Generally, implementation of MRRMoptimizes the usage of resources and minimizes the costs. However, suchMRRM algorithms require access specific knowledge, e.g. the capacity andload in different radio cells belonging to different accesstechnologies, and the link characteristics and quality for differentaccess links of a user. For this reason, most MRRM studies suggest anarchitecture, where (one or more) MRRM functions collect all requiredaccess resource information of the different access technologies todetermine the best allocation of users to access technologies. From thatperspective, multi-access is achieved by connecting multiple differentaccess networks to a common multi-access network.

In most standardisation activities the approach of multi-accessintegration differs from the previous described approach. There, it isinstead assumed that different access networks remain independent andare connected to a common core network.

An exception is the concept of Common Radio Resource Management (CRRM)inter-system handover between the GSM/EDGE Radio Access Network (GERAN)and the Universal Terrestrial Radio Access Network (UTRAN) discussed andpartly specified by the third Generation Partnership Project (3GPP).

In the prior art all access specific knowledge is supposed to remainwithin each access network and the core network is supposed to stayagnostic of any radio- or access specific knowledge, or load informationon individual cell level is handled in a CRRM server that is sharedbetween two radio access networks, which is one of the solutionsdiscussed in 3GPP.

There are several reasons for keeping the core network agnostic toaccess-level information. One is, for example, the problem ofscalability if access knowledge on cell level, or even at finergranularity, would be exported into the core network. Another reason isthat use of the core network may be extended to new access technologies,as it does not need to be aware of access technology specifics. Afurther reason is that the core network may belong to another operator(administrative domain), whereby access specific information is notdesired to be exposed to the core network. Consequently, the gains ofMRRM cannot be easily achieved in an approach combining different accesstechnologies in the core network.

SUMMARY OF THE INVENTION

Accordingly, it is an objective with the present invention to provide animproved method for making a handover decision in a multi-accesscommunication network comprising a core network and at least one userterminal network communicating with said core network on at least twoaccess paths via at least two access networks, whereby data sessions arerouted on at least a first access path via a first access network and asecond access path via a second access network.

This objective is achieved through a method comprising the steps of:determining a first set of criteria for when a handover between said atleast two access paths should be performed; sending a first report whenat least one criterion of said first set of criteria is fulfilled;determining a second set of criteria for when a handover between said atleast two access paths should be performed; sending a second report whenat least one criterion of said second set of criteria is fulfilled;determining one or more data sessions of said at least one user terminalnetwork to be handed over based on at least one of the sent first andsecond report; and, executing a handover by re-routing said determineddata sessions from one access path to an alternative access path.

Another objective of the present invention is to provide an improvedarrangement for making a handover decision in a multi-accesscommunication network comprising a core network and at least one userterminal network communicating with said core network on at least twoaccess paths via at least two access networks, whereby data sessions arerouted on at least a first access path via a first access network and asecond access path via a second access network.

This other objective is achieved through providing an arrangementcomprising: means for determining a first set of criteria for when ahandover between said at least two access paths should be performed;means for sending a first report when at least one criterion of saidfirst set of criteria is fulfilled; means for determining a second setof criteria for when a handover between said at least two access pathsshould be performed; means for sending a second report when at least onecriterion of said second set of criteria is fulfilled; means fordetermining one or more data sessions of said at least one user terminalnetwork to be handed over based on at least one of the sent first andsecond report; and, means for executing a handover by re-routing saiddetermined data sessions from one access path to an alternative accesspath.

A further objective of the present invention is to provide a computerprogram product, which is directly loadable into the internal memory ofa digital computer, and which comprises a computer program forperforming the method when said program is run on said computer.

Thanks to the provision of distributed access selection functionalityonto a number of different entities, the gains of MRRM is achieved,while allowing the common network nodes to remain agnostic of accessspecifics that are part of the MRRM algorithm. Thus, a lightweight andscalable realisation of MRRM is provided, which provides accessselection outside the access networks and where access selection can belocated in the core network, in an independent network, or even in auser terminal network.

The arrangement and the method according to the present invention may beused to provide multi-access resource management within the multi-accessapproach currently defined within 3GPP System Architecture Evolution.

Still other objects and features of the present invention will becomeapparent from the following detailed description considered inconjunction with the accompanying drawings. It is to be understood,however, that the drawings are designed solely for purposes ofillustration and not as a definition of the limits of the invention, forwhich reference should be made to the appended claims. It should befurther understood that the drawings are not necessarily drawn to scaleand that, unless otherwise indicated, they are merely intended toconceptually illustrate the structures and procedures described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, wherein like reference characters denote similarelements throughout the several views:

FIG. 1 shows a schematic block diagram over the network architecturewith an access selection functionality distribution according to oneembodiment of the present invention;

FIG. 2 shows a schematic block diagram over the network architecturewith an access selection functionality distribution according to anotherembodiment of the present invention;

FIG. 3 is a schematic block diagram over an exemplary hardwareimplementation of an Access Network control Function (ANF) node;

FIG. 4 is a schematic block diagram over an exemplary hardwareimplementation of a Connection Management Function (CMF) node in a UserTerminal Network (UTN);

FIG. 5 is a schematic block diagram over an exemplary hardwareimplementation of the Connection Management Function (CMF) node in aUser Terminal Network (UTN) device;

FIG. 6 is a schematic block diagram over an exemplary hardwareimplementation of an Access Selection Function (ANF) node;

FIG. 7 is an exemplary flowchart showing the steps taken in the AccessNetwork Function (ANF) node;

FIG. 8 is an exemplary flowchart showing the steps taken in theConnection Management Function (CMF) node;

FIG. 9 is an exemplary flowchart showing the steps taken in the AccessSelection Function (ASF) node.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

This invention strongly applies to access technologies and accessnetworks based on radio transmission (e.g. wireless, mobile or cellularnetworks). However, this invention also applies to other accesstechnologies and access networks (e.g. fixed access). Although thedescription of this invention sometimes refers to radio access, radiotechnology, radio resource management, radio access network etc, it canbe applied to any kind of access technologies and access networks.

FIG. 1 shows a User Terminal Network, UTN, 10 which is within thecoverage of a first access network 20 a and a second access network 20 band has two access paths a, b to the core network 30. The access paths aand b connects a core network anchor 32 and a terminal anchor 12. Eachaccess path a, b goes via one access network (AN) 20 a, 20 b andcomprises at least one transmission link 15 a, 15 b. In Radio AccessNetworks, the link 15 a, 15 b is also called Radio Access (RA). The corenetwork anchor 32 and the terminal anchor 12 are arranged to route dataof the UTN data sessions to a selected access path a and/or b.

The UTN 10 may be a single device or a complete network that isconnected to the core network 30 via fixed or wireless access. It couldbe, e.g., a personal area network, consisting of several devices thatare interconnected via some short-range communication. It could also bea larger network connected via a common gateway to the wireless network.What is important, is that the UTN 10 can be identified by the corenetwork 30, e.g., by means of an access identifier.

The main idea of this invention is to distribute the access selectionfunctionality onto a number of different entities. The final accessselection decision is taken in an entity called Access SelectionFunction (ASF) 34, and it is not directly based on access specificknowledge, cell level topology/load information, nor access specificlink measures. The access-specific part of access selection is providedby two other functions. Each user terminal—or more general, UserTerminal Network (UTN) 10 in case of multiple connected devices—containsa Connection Management Function (CMF) 14, which determines theavailability of different access links 15 a, 15 b, the characteristicsof the access links 15 a, 15 b, as well as, the resource usageassociated with each access link 15 a, 15 b. Almost each access network20 a, 20 b further contains an Access Network Control Function (ANF) 25a, 25 b which determines the load and capacity of radio cells, thecharacteristics of access links 15 a, 15 b and for each user terminalnetwork 10, the resource costs of an access link 15 a, 15 b. However,there might be access networks that do not comprise an ANF, e.g. fixedaccess networks. The ANF 25 a, 25 b and CMF 14 manage in a preferredembodiment of the present invention the access specific part of an MRRMalgorithm in a distributed manner. Only if critical situations aredetected in either of the access networks 20 a, 20 b or the userterminal network 10, the ASF 34 is triggered with sufficient (stillaccess agnostic) information to make access selection decisions.

A common realization is that ASF is part of the Core Network Anchor.But, according to the present invention it is described here as aseparate function that may be located in a separate node as depicted inFIG. 1, but may as well be located in another network. As can be seen inFIG. 1, the ASF 34 is communicating with the ANFs 25 a, 25 b and the CMF14 by receiving information reports and sending requests of updatedreports (shown with broken arrows) and, is controlling the core networkanchor 32 and the terminal anchor 12 (shown with continuous arrows) toperform the selected handovers.

FIG. 2 shows another embodiment of the present invention, in which theASF 34 is implemented in the user terminal network 10 instead of in thecore network 30. Thus, FIG. 2 shows a UTN, 10 which is within thecoverage of a first access network 20 a and a second access network 20 band has two access paths a, b to the core network 30. The access paths aand b connects a core network anchor 32 and a terminal anchor 12. Eachaccess path a, b goes via one access network 20 a, 20 b and comprises atleast one transmission link 15 a, 15 b. The core network anchor 32 andthe terminal anchor 12 are arranged to route data of the UTN datasessions to a selected access path a and/or b. The ASF 34 iscommunicating with the ANFs 25 a, 25 b and the CMF 14 by receivinginformation reports and sending requests of updated reports (shown withbroken arrows) and is controlling the core network anchor 32 and theterminal anchor 12 (shown with continuous arrows) to perform theselected handovers.

For simplicity, FIGS. 1 and 2 show only one UTN 10 and two accessnetworks 20 a and 20 b. However, the multi-access system may of coursecomprise several access networks and comprises usually a plurality ofuser terminal networks. Alternatively, the system comprises a singleaccess network comprising different access nodes for different accesstechnology or, even, the same access technology. One or more UTNs mayconnect to at least two of these nodes/technologies, independent ofwhich access network/access technology they relate to, in such a waythat they overlap in coverage. The access nodes do not coordinate accessselection among each other, this is done by the ASF. So, there are atleast two access paths which are not directly coordinated by theinvolved access nodes. In this context, at least two access networksshould be understood to mean at least two separate access networks, atleast two access nodes in an access network or a combination thereof.

The access network function 25, the connection management function 14and the access selection function 34, will now be described in greaterdetail.

Access Network Function (ANF)

The Access Network Function 25, shown in FIG. 3, performs the followingfunctions:

-   -   observing the performance (e.g. data rate, delay, delay jitter,        error rate) of an access path a or b (shown in FIGS. 1 and 2).        In many systems the performance and resource efficiency of an        access path is dominated by a few hops, typically the first hops        connecting the UTN to the fixed network. In these cases it is        common, that not the performance and resource efficiency of the        complete access path is observed, but instead only the        performance and resource usage of the dominating hops are used        as a measure for the complete access path. Examples for such        systems are wireless networks, multi-hop networks or narrow-band        fixed access networks; in all these cases the performance of the        access path is determined largely by the performance of the        first access hops;    -   observing the resource usage (e.g. transmission power,        processing power and memory usage) for an access path;    -   monitoring the fulfillment of the required service performance        for data sessions;    -   observing if new access paths are detected and/or established;    -   observing if access paths are lost or disconnected;    -   observing the resource usage/load of the access network (e.g.        traffic load in the transport network, traffic load in different        cells, capacity/usage/efficiency of access specific resources        {transmission power, processing power, used time        slots/codes/carriers}, queue fill states, cell interference) and        variations of the usage;    -   updating the ASF 34 with “critical” information related to        access paths in so-called ANF report messages. These ANF reports        can be sent event-triggered, e.g. whenever a critical situation        as defined below is detected or ceases to be critical, or        periodically, or in a combination of periodic and        event-triggered reporting.

The access network comprises an access network control node 22containing measurement and control functions 24, which give input to anANF processor 26 located in the ANF node 25. The input given is accessspecific information, such as cell load and available resources, linkquality, processing load, etc. An optional input is a request from theASF to send updated ANF message.

The Access Network Function 25 defines a first set of criteria for“critical” situations that may trigger a handover:

-   -   1. If the cell load or number of available resources becomes        critical (e.g. exceeding or falling below a threshold value);    -   2. If the processing load or AN transmission network load        becomes critical (e.g. exceeding or falling below a threshold        value);    -   3. If for a user terminal the handovers becomes critical (e.g.        exceeding or falling below a threshold value);    -   4. If the link quality of an access link becomes critical (e.g.        exceeding or falling below a threshold value), a Quality of        Service (QoS) requirement cannot be met, or the resource costs        for an access link become too expensive.

A handover may be triggered if a situation becomes “critical” but may aswell be triggered if the situation stops to be critical.

A handover is in this context defined as switching at least one datasession belonging to a user terminal network from one access path toanother access path.

The critical situations 1 and 2 apply for all user terminal networksthat are affected by the critical situation, e.g. all UTNs within theoverloaded cell (in case of 1) or all UTNs connected to the overloadednetwork and/or network node (in case of 2). The critical situations 3and 4 apply for certain data sessions of a specific UTN, or the UTN as awhole.

If such a critical situation is detected or the critical situationbecomes uncritical again, the ANF 25 reports to the Access SelectionFunction (ASF) 34 in an ANF report. This report does not contain accessspecific information, which would require an understanding of thedetails of the access technology. It only contains, a list of userterminal network identifiers which are affected by the “critical (e.g.overload) situation” and, thus, become potential candidates for ahandover action. It possibly also contains session flow identifiers incase only certain data sessions of a user terminal network are to beconsidered for a handover. It is also possible that the message containsan area identifier, describing in which area of the AN an overloadoccurs. Some form of location (possibly in an AN specific form likelocation area identifier) is available in the core network and ASF, e.g.for reachability of the user terminal network. An area identifier allowsthe ASF to identify all UTNs that are affected by the criticalsituation. Such an ANF report could e.g. indicate “there is an overloadin cells {x,y} of AN A”, and the ASF could identify the user terminalswhich are located in this area. Alternatively, if an overload situationaffects a certain area, the ANF function could translate the areainformation into a list of UTN that are located in this area. The ANFreport then only contains the UTN identifiers. The ANF report mayfurther contain a type field, indicating the type of critical situation,with access specifying parameters. The ANF report may comprise anindication of the how critical the situation is, e.g. in a scale from0-100.

In case that the ANF translates overload related to an area into an ANFreport message that lists individual UTNs/data sessions, the ANF mayapply some filtering depending on how critical the situation is. Forexample, if the load of a cell only slightly exceeds a load limit, theANF can select only a limited subset of the affected UTNs in the cell,and report only an ANF report for this limited subset of UTNs to theASF. For determining the subset, access specific information can beused, e.g. to select the UTNs which require comparatively high resourcesfor a certain transmission performance. A realization could be, that theANF selects a list of UTNs to be reported, sorted according to somecriteria (like resource consumption, priority, etc.) and indicates howmany or what percentage of the listed UTNs should be handed over. TheASF can then make the selection based on the ANF information report.

Further, the resource costs of the UTNs may be weighted in the ANFreport. E.g. the ANF report could report 4 UTNs with resource weight Wassigned {UTN1, W1=7}, {UTN2, W2=3}, {UTN3, W3=2}, {UTN4, W4=2}. Ifthere is a need for a resource cost reduction of a total weight of 7,the ASF may achieve this demand by either select only UTN1 or select theother three UTNs (UTN1+UTN2+UTN3).

Typically the ANF is collocated or integrated with the access networkspecific control node which manages the access resources (e.g. UMTSradio network controller, WLAN Access Point Controller, etc).

Connection Management Function (CMF)

The Connection Management Function 14, shown in FIGS. 4 and 5 performsthe following functions:

-   -   observing the performance (e.g. data rate, delay, delay jitter,        error rate) of an access path a or b. In many systems the        performance and resource efficiency of an access path is        dominated by a few hops, typically the first hops connecting the        UTN to the fixed network. In these cases it is common, that not        the performance and resource efficiency of the complete access        path is observed, but instead only the performance and resource        usage of the dominating hops are used as a measure for the        complete access path. Examples for such systems are wireless        networks, multi-hop networks or narrow-band fixed access        networks; in all these cases the performance of the access path        is determined largely by the performance of the first access        hops;    -   observing the resource usage (e.g. transmission power,        processing power and memory usage) for an access path a or b;    -   monitoring the fulfillment of the required service performance        for data sessions;    -   observing if new access paths are detected and/or established;    -   observing if access paths are lost or disconnected;    -   updating the ASF with “critical” information related to access        paths in so-called CMF report messages. These CMF reports can be        sent event-triggered, e.g. whenever a critical situation as        defined below is detected or ceases to be critical, or        periodically, or in a combination of periodic and        event-triggered reporting.

The CMF 14 may be a separate node in the UTN as shown in FIG. 4, inwhich a CMF processor 18 located in the CMF node 14 receive input frommeasurement and control functions 17 comprised in a UTN device 16.Received input may be performance of available access paths, resourceusage of available access paths, changes in available access paths,handover events, etc. Optionally, the CMF processor 18 receives arequest from the ASF 34 to send an updated CMF message.

Alternatively as shown in FIG. 5, The CMF 14, i.e. the CMF processor 18is implemented in a UTN device 16 comprising measurement and controlfunctions 17, which gives input to the CMF processor 18, and also otheruser terminal functionalities 19. The CMF processor 18 may also receiveinput from measurement and control functions 17 comprised in another UTNdevice 11. Received input may be performance of available access paths,resource usage of available access paths, changes in available accesspaths, handover events, etc. Optionally, the CMF processor 18 receives arequest from the ASF 34 to send an updated CMF message.

The CMF defines a second set of criteria for “critical” situations forone or more data sessions of a UTN or the UTN as a whole that may berelevant for a handover decision:

-   -   If the access link quality of one or more access links changes;    -   If a new access link is detected;    -   If a service requirement cannot be met by the current access        link;    -   If too many handovers occur at the current access technology;    -   If the resource costs (processing, battery, power, price of        usage) are too high;    -   If large interference is detected for an access link.

A handover may be triggered if a situation becomes “critical” but may aswell be triggered if the situation stops to be critical.

If such a critical situation is detected (or a situation stops to becritical), the CMF reports this to the Access Selection Function (ASF)34 in a CMF report message. This CMF report contains user terminalnetwork identifiers, and possibly session flow identifiers (if only somesessions are to be handed over), identifying for which UTNs/sessions thecritical situation applies. Further, it contains what type of criticalsituation has been detected (e.g. from the above list) and possiblyfurther parameters specifying the situation. These parameters do notcontain access specific information valid only for a certain type ofaccess technology. Instead some access-agnostic information is used.This may e.g. be parameters specified in access-agnostic units (expecteddata rate in kb/s; delay in ms, etc.) or parameters given in anormalized measure, e.g. normalized in a range from 0-100. The CMFreport message may further comprise an indication of the how criticalthe situation is, e.g. in a scale from 0-100.

In addition the CMF informs ASF when new access links are detected andwhen these access links are established.

Access Selection Function (ASF)

The Access Selection Function 34, shown in FIG. 6, manages an ASFdatabase 36 for multiple user terminal networks. In this database 36 thefollowing information is stored for each UTN:

-   -   UTN identifier;    -   List of access paths for this user terminal network. For each        access path the following information is stored:        -   Optionally: identifier of core network anchor and terminal            anchor used for this access path and the corresponding            access path routing method (e.g. mobile IP; hierarchical            mobile IP; mobility and multi-homing protocol (MOBIKE); GPRS            Tunnelling Protocol (GTP));        -   Access path identifier. This can be, for example, a locator            (e.g. IP care of address for mobile IP; tunnel endpoint            identifier; or a combination of: RAN identifier, RAN access            node identifier and RAN specific UTN identifier);        -   Optionally: type of access used for access path (e.g. WLAN,            GPRS, UMTS, HSPA, DSL, Ethernet);        -   Characteristics of access path, like e.g., peak rate,            average rate, delay, security support, QoS support. The            characteristics parameters can have a time stamp associated            to them, indicating when the last update of a parameter was            made;        -   Optionally: area identifier;        -   Optionally: marker indicating that the access path is marked            as critical. The marker can have an associated time stamp            (showing when the access path was marked as critical) and a            time period (indicating how long this marking is valid);        -   Optionally: handover frequency.    -   List of sessions. For each session the following information is        stored:        -   Session requirements, e.g. QoS requirements (delay, rate,            etc.); security requirements;        -   Active access path(s). A session may be also mapped to            multiple access paths in parallel.

It may be that all sessions of a UTN shall always be mapped to the sameaccess path. In this case this information does not need to be storedper session but only for the UTN as such.

The task of the ASF is to:

-   -   Select the best suited access path for UTNs. Hereby the sessions        of UTNs are mapped to access paths;    -   Update the core network anchor and user terminal anchor        accordingly, such that the binding of session flows to access        paths is set accordingly;    -   Receive information from ANFs and CMFs which is relevant for the        access path selection function;    -   Query information from ANFs and CMFs, which report back to the        ASF information that is relevant for the access path selection        function;    -   Update the ASF database accordingly when information is received        by CMFs (CMF report) and/or ANFs (ANF report);    -   Update the ASF database when a handover of access paths is        decided.

In order to be able to achieve the task, a ASF processor 35 located inthe ASF node 34 receives input from the ANF 25 and the CMF 14.

When the ASF receives an ANF report from an ANF 25 or a CMF report froma CMF 14 it performs the following functions:

-   -   It identifies all possibly affected UTNs and sessions. Affected        UTNs and sessions can be explicitly listed within the message.        Also an area identifier can be included in the message,        indicating that all UTNs with an access path related to this        area identifier are affected;    -   It identifies for affected UTNs/sessions possible handover        options, i.e. possible alternative access paths are identified.        A special form of handover is, if a terminal does not have an        alternative access path. If a request by ANF is received to make        a handover for this user (e.g. since he uses too much access        resources) his session may be dropped. A pre-emption by ANF may        not be feasible, since each ANF does not know if alternative        access paths for this UTN exist;    -   Establish a list of all possible handover options for all        affected UTNs/sessions;    -   Optionally: request from ANF and/or CMF information status of        candidate access paths. For candidate access paths some        parameters may not have been updated recently (which can be        determined from a time stamp associated with each parameter        update);    -   Sort the list of possible handover actions in priority order,        based on a combination of (at least some of) the following        criteria:        -   Policies (user subscription). Some users may have a premium            subscription, which allows them to be served at a higher            quality level and/or higher priority;        -   Availability of alternative access paths for this user            terminal network;        -   Service requirement and capabilities of alternative access            path;        -   Severity of action for this UTN/session. The severity can be            defined to what extent the session requirements are met. If            even minimum requirements are not met a handover is            classified as very severe. Similarly, if no alternative            access path exists and the only possible handover is to drop            the session this is classified as very severe. Session            requirements can be QoS-related as well as other            requirements, like security requirements.    -   Perform the handover from that list in order of priority until a        threshold of required actions is met.

Often a handover decision is triggered when the access pathcharacteristics for a single UTN change (this can be triggered by CMF orANF). In this case, the sorted list of handover actions lists thepossible handover options for this UTN, where the first element givesthe handover to the “best” alternative access path. If a handoverdecision is triggered when the load of a certain cell passes athreshold, the sorted list of handover actions lists possible handoveroptions for all UTNs located in the overloaded cell. In this case it isnot required that all UTNs perform a handover, but only a number of UTNssuch that the total cell load decreases again. How many UTNs need toperform a handover can be determined from a parameter in the ANF report,which tells how critical the load situation is. This parameter can e.g.indicate, what percentage of the UTNs affected by this ANF report shallbe handed over.

The handover execution is performed by directing the Core Network Anchor32 and User Terminal Network Anchor 12 nodes to perform the handover.I.e. access path switching functions 38 and 13 in the core networkanchor 32 and the UTN anchor 12 respectively, receives output from theASF processor 35 about the handover. The Core Network Anchor 32 and UTNAnchor 12 may both support different procedures/protocols for performinga handover, e.g. based on Mobile IP, GTP, a local binding, etc. Theappropriate procedure and corresponding access path identifiers areprovided by ASF.

A first set of criteria for when a handover between at least two accesspaths should be performed is determined by the ANF and a second set ofcriteria for when a handover between at least two access paths should beperformed is determined by the CMF. There may further be a third set ofcriteria for when a handover between at least two access paths should beperformed, e.g. when a policy rule changes. This could be:

-   -   a UTN has used up all credits for using a certain access network        or access technology;    -   the authorization for usage of an access network or access        technology has been revoked;    -   the user priority has changed;    -   the access networks change their rules of sharing resources with        other access networks;    -   the price of usage for an access network has changed.

In a preferred embodiment of the present invention, the procedure in theAccess Network Function (ANF), shown in FIG. 7, is as follows:

-   -   receiving access specific information, such as cell load and        available resources, processing load and link quality from the        access network control node (step 71);    -   comparing the received information against criteria for        “critical” situations (step 72), i.e. if the cell load or number        of available resources becomes critical, if the processing load        or AN transmission network load becomes critical, if for a user        terminal the handover frequency becomes critical or if the link        quality of an access link becomes critical;    -   if no critical criterion is fulfilled, going back to step 71;    -   if any critical criterion is fulfilled, determining an        indication of how critical the situation is (step 73);    -   determining affected UTNs and possibly relevant sessions of a        UTN (step 74) and deriving a list of affected UTNs and/or        sessions;    -   optionally, pre-filtering derived list of affected UTNs and/or        sessions (step 75);    -   sending ANF message to ASF containing relevant UTNs and/or        sessions (possibly pre-filtered), area identifiers and, an        indication of how critical the situation is;    -   if the ANF receives a request from the ASF for an update message        or if the ANF message is periodically sent to the ASF,        performing steps 74-76 as shown on the left hand side of FIG. 7.

In a preferred embodiment of the present invention, the procedure in theConnection Management Function (CMF), shown in FIG. 8, is as follows:

-   -   receiving measurements on access paths, such as performance,        resources and events (step 81);    -   comparing the received information against criteria for critical        situations (step 82), i.e. if the access link quality of one or        more access links changes, if a new access link is detected, if        a service requirement cannot be met by the current access link,        if too many handovers occur at the current access technology, if        the resource costs (processing, battery, power) are too high or,        if large interference is detected for an access link;    -   if no critical criterion is fulfilled, going back to step 81;    -   if any critical criterion is fulfilled, determining an        indication of how critical the situation is (step 83);    -   determining affected relevant sessions (step 84);    -   determining additional access agnostic parameters, e.g. bit rate        in kb/s (step 85); and,    -   sending CMF message to ASF (step 86) containing UTN identifier,        possibly relevant sessions, type of critical situation or if it        is a periodical update, possibly additional access agnostic        parameters specifying the update/status, such as data rate in        kb/s, and, possibly an indication of how critical the situation        is;    -   if the CMF receives a request from the ASF for an access path        status update message or if the CMF message is periodically sent        to the ASF, performing steps 84-86 as shown on the left hand        side of FIG. 8.

In a preferred embodiment of the present invention, the procedure in theAccess Selection Function (ASF), shown in FIG. 9, is as follows:

-   -   receiving ANF and CMF messages (step 91). The ANF message        containing relevant UTNs and/or sessions (possibly        pre-filtered), area identifiers and, an indication of how        critical the situation is. The CMF message containing UTN        identifier, possibly relevant sessions, type of critical        situation or if it is a periodical update, possibly additional        access agnostic parameters specifying the update/status, such as        data rate in kb/s, and, possibly an indication of how critical        the situation is;    -   updating ASF database (step 92) with received information;    -   identifying affected UTNs and/or sessions, i.e. candidates for        handovers (step 93) using relevant information from the        database;    -   checking if sufficient information for access selection is        available and if parameters are up-to-date. If the check not is        successful, requesting updating reports from one or more ANF        and/or one or more CMF, i.e. going back to step 91;    -   identifying sorted list of handover options, i.e. possible        alternative access paths, in priority order (step 94), using        relevant information from the database;    -   selecting first handover (UTN and/or sessions) in sorted list        and remove that handover from list (step 95);    -   performing handover of the selected UTN and/or session by        updating the core and UTN anchors to bind session flows to new        access path (step 96);    -   as long as a pre-determined threshold of requested handovers is        not reached, selecting the first handover in the sorted list        (step 95);    -   when the pre-determined threshold of requested handovers is        reached, updating the ASF database (step 97).

Thus, according to a preferred embodiment of the present invention, themethod for making a handover decision in a multi-access communicationnetwork comprising a core network and at least one user terminal networkcommunicating with said core network on at least two access paths via atleast two access networks, whereby data sessions are routed on at leasta first access path via a first access network and a second access pathvia a second access network, comprises the following steps of:

-   -   determining a first set of criteria for when a handover between        said at least two access paths should be performed;    -   sending a first report when at least one criterion of said first        set of criteria is fulfilled;    -   determining a second set of criteria for when a handover between        said at least two access paths should be performed;    -   sending a second report when at least one criterion of said        second set of criteria is fulfilled;    -   determining one or more data sessions of said at least one user        terminal network to be handed over based on at least one of the        sent first and second report;    -   executing a handover by re-routing said determined data sessions        from one access path to an alternative access path.

The present invention also comprises a computer program product, whichis directly loadable into the internal memory of a digital computer, andwhich comprises a computer program for performing the inventive methodwhen said program is run on said computer.

Thus, while there have been shown and described and pointed outfundamental novel features of the invention as applied to a preferredembodiment thereof, it will be understood that various omissions andsubstitutions and changes in the form and details of the devicesillustrated, and in their operation, may be made by those skilled in theart without departing from the spirit of the invention. For example, itis expressly intended that all combinations of those elements and/ormethod steps which perform substantially the same function insubstantially the same way to achieve the same results are within thescope of the invention. Moreover, it should be recognized thatstructures and/or elements and/or method steps shown and/or described inconnection with any disclosed form or embodiment of the invention may beincorporated in any other disclosed or described or suggested form orembodiment as a general matter of design choice. It is the intention,therefore, to be limited only as indicated by the scope of the claimsappended hereto.

1. An arrangement for making a handover decision in a multi-accesscommunication network comprising a core network and at least one userterminal network communicating with said core network on at least twoaccess paths via at least two access networks, whereby data sessions arerouted on at least a first access path via a first access network and asecond access path via a second access network, wherein the arrangementcomprises: means for determining a first set of criteria for when ahandover between said at least two access paths (a, b) should beperformed; means for sending a first report when at least one criterionof said first set of criteria is fulfilled; means for determining asecond set of criteria for when a handover between said at least twoaccess paths a, b should be performed; means for sending a second reportwhen at least one criterion of said second set of criteria is fulfilled;means for determining one or more data sessions of said at least oneuser terminal network to be handed over based on at least one of thesent first and second report; means for executing a handover byre-routing said determined data sessions from one access path to analternative access path.
 2. An arrangement according to claim 1, whereinsaid means for determining the first set of criteria is an accessnetwork control function located in at least one of said at least twoaccess networks.
 3. An arrangement according to claim 1, wherein saidmeans for determining the second set of criteria is a connectionmanagement function located in said at least one user terminal network.4. An arrangement according to claim 1, wherein said means fordetermining one or more data sessions of said at least one user terminalnetwork to be handed over is an access selection function.
 5. Anarrangement according to claim 4, wherein said access selection functionis located in the core network.
 6. An arrangement according to claim 4,wherein said access selection function is located in the user terminalnetwork.
 7. An arrangement according to claim 4, wherein said accessselection function is arranged to request for first and second reports.8. An arrangement according to claim 4, wherein said access selectionfunction comprises means for establishing a list of possible saidhandover actions for affected user terminal network data sessions andmeans for sorting said list in priority order, whereby handovers areexecuted from said list in priority order until a threshold of requiredhandover actions is met.
 9. An arrangement according to claim 1, whereinthe arrangement further comprises means for determining a third set ofcriteria for when a handover between said at least two access pathsshould be performed.
 10. An arrangement according to claim 1, whereinsaid at least two access networks are at least two access network nodeslocated in one access network.
 11. An arrangement in an access networkfor making a handover decision in a multi-access communication networkcomprising a core network and at least one user terminal networkcommunicating with said core network on at least two access paths via atleast two access network nodes, whereby data sessions are routed on atleast a first access path via a first access network node and a secondaccess path via a second access network node, wherein the arrangementcomprises: means for determining a set of criteria for when a handoverbetween said at least two access paths should be performed; means forsending a report to a superior access selection function node when atleast one criterion of said set of criteria is fulfilled, whereby saidaccess selection function node is arranged to determine one or more datasessions of said at least one user terminal network to be handed overbased on said sent report.
 12. An arrangement in a user terminal networkfor making a handover decision in a multi-access communication networkcomprising a core network and at least one user terminal networkcommunicating with said core network on at least two access paths via atleast two access networks, whereby data sessions are routed on at leasta first access path via a first access network and a second access pathvia a second access network, wherein the arrangement comprises: meansfor determining a set of criteria for when a handover between said atleast two access paths should be performed; means for sending a reportto a superior access selection function node when at least one criterionof said set of criteria is fulfilled, whereby said access selectionfunction node is arranged to determine one or more data sessions of saidat least one user terminal network to be handed over based on said sentreport.
 13. An access selection function for making a handover decisionin a multi-access communication network comprising a core network and atleast one user terminal network communicating with said core network onat least two access paths via at least two access networks, whereby datasessions are routed on at least a first access path via a first accessnetwork and a second access path via a second access network, whereinthe access selection function comprises: means for receiving a report ifat least one criteria for when a handover between said at least twoaccess paths should be performed is determined means for determining oneor more data sessions of said at least one user terminal network to behanded over based on said sent report whereby a handover is executed byre-routing said determined data sessions from one access path to analternative access path.
 14. An access selection function according toclaim 13, wherein said access selection function is located in the corenetwork.
 15. An access selection function according to claim 13, whereinsaid access selection function is located in the user terminal network.16. A method for making a handover decision in a multi-accesscommunication network comprising a core network and at least one userterminal network communicating with said core network on at least twoaccess paths via at least two access networks, whereby data sessions arerouted on at least a first access path via a first access network and asecond access path via a second access network wherein the methodcomprises the steps of: determining a first set of criteria for when ahandover between said at least two access paths should be performed;sending a first report when at least one criterion of said first set ofcriteria is fulfilled; determining a second set of criteria for when ahandover between said at least two access paths should be performed;sending a second report when at least one criterion of said second setof criteria is fulfilled: determining one or more data sessions of saidat least one user terminal network to be handed over based on at leastone of the sent first and second report; executing a handover byre-routing said determined data sessions from one access path to analternative access path.
 17. A method according to claim 16, wherein thestep of determining a first set of criteria is performed by an accessnetwork control function located in at least one of said at least twoaccess networks.
 18. A method according to claim 16, wherein the step ofdetermining a second set of criteria is performed by a connectionmanagement function located in said at least one user terminal network.19. A method according to claim 16, wherein the step of determining oneor more data sessions of said at least one user terminal network to behanded over is performed by an access selection function.
 20. A methodaccording to claim 16, wherein the method further comprises the step ofdetermining a third set of criteria for when a handover between said atleast two access paths should be performed.
 21. A method according toclaim 19, wherein said first and second reports are sent upon request bysaid access selection function.
 22. A method according to claim 19,wherein said first and second reports are sent periodically to saidaccess selection function.
 23. A method according to claim 16, whereinthe method further comprises the steps of: establishing a list ofpossible said handover actions for affected user terminal network datasessions; and, sorting said list in priority order, whereby handoversare executed from said list in priority order until a threshold ofrequired handover actions is met.
 24. A computer program product, whichis directly loadable into the internal memory of a digital computer, andwhich comprises a computer program for performing the method of claim 16when said program is run on said computer.